This invention relates to a noise preventing or reducing means used in disc brakes, more particularly to an improvement of a noise reducing means of the type wherein a plate member is inserted between the friction pad and the piston which urges the same.
In disc brakes of the type in which a friction pad is urged, with a piston working in an hydraulic cylinder, onto a disc rotating together with the wheels or others in order to halt the disc, unpleasant or disagreeable noises sometimes occur, among which the noise named "squeal of the brake" is most unpleasant, and various attempts have been made for the prevention thereof.
As one of those attempts, U.S. Pat. No. 3,113,643 is widely known for its effectiveness in reducing the noise. The essence of this prior art invention lies in the insertion of a shim or a plate member between the friction pad and the piston, which plate member being partially cut out an elongatedly extending arcuate aperture at a location wherein the same confronts with the inner end of the piston on the side the rotating disc first comes into alignment therewith.
Concerning the reasoning for the good effects of the insertion of such a plate member (hereinafter simply referred to as cut-out shim), the above cited U.S. Pat. No. 3,113,643 discloses as follows:
(1) Experiments indicate that one of the causes of squeal which is liable to occur when the friction pad is applied to the disc is the rigidity of the engagement between the piston and the backing plate of the pad.
According to my invention, in a brake or clutch of the kind set forth, the piston is arranged to engage the backing plate of the friction pad over an area which is not symmetrical with respect to the axis of the hydraulic cylinder.
(2) Tests have shown that it is preferable to cut out the shim or step or set back the piston or backing plate on the side of the axis of the cylinder or the center of the friction pad with which any given point on the disc first comes into alignment, so that the center of the area of contact between the piston and the backing lies on the other side of the axis of the cylinder or the center of the pad. This assists in ensuring substantially even wear of the pad over the whole of its area.